Pentadienyl-metal-phosphine chemistry. XXI. Synthesis and characterization of electron-rich (pentadienyl)iron[1,2-bis(diethylphosphino)ethane] complexes

Treatment of (Cl)₂Fe(depe)₂ (depe = Et₂PCH₂CH₂PEt₂) with two equivalents of potassium pentadienide produces (η³-pentadienyl)₂Fe(depe) (1). Compound 1 crystallizes in the orthorhombic space group Pbcn (No. 60) with a = 11.347(1), b = 0.718(2), c = 19.938(3) Å, V = 2198.6(6) ų, and Z = 4. In the solid state structure of 1, both η³-pentadienyl ligands are syn and W-shaped; however, in solution the major "syn,syn" isomer exists in equilibrium with a minor "syn,anti" isomer. Treatment of compound 1 with one equivalent of protonated depe (Hdepe⁺ BF^-₄) leads to loss of trans-1,3-pentadiene and production of (η³-pentadienyl)Fe(depe)⁺₂ BF^-₄ (2). Compound 2 crystallizes in the triclinic space group P1 (No. 1) with a = 10.070(2), b = 10.756(1), c = 8.3622(1) Å, α = 112.04(2), β = 94.93(1), γ = 68.05(1)°, V = 777.1(3) ų, and Z = 1. In the solid state structure of 2, the η³-pentadienyl ligand has a syn geometry and is W-shaped. In solution, the syn-η³-pentadienyl complex exists in equilibrium with its anti-η³-pentadienyl isomer.